Projection display systems based on liquid-crystal-on-silicon (“LCoS”) microdisplay technology commonly employ one, two, or three LCoS imaging panels in order to create a full color projected image. When three panels are used, each panel is illuminated with one of the three primary colors. Each panel is electronically addressed with video data corresponding to the color channel for the illuminating light received at that imager. Finally these three monochrome images are projected onto the screen simultaneously, resulting in a high brightness image that has no artifacts associated with temporal color sequencing of the image data.
In one panel systems, such as those disclosed in U.S. Pat. No. 6,702,446 issued Mar. 9, 2004 to De Vaan et al, and U.S. Pat. No. 6,707,516 issued Mar. 16, 2004 to Johnson et al, some means of illuminating the single imager is employed, typically either color-sequencing or scrolling a pattern of three primary-colored stripes of light across the imager to create a full color image. The imager is electronically addressed with a time-sequential (and possibly scrolling) video image data stream that modulates in synchrony with the time—(and possibly space—) varying multi-color illumination source.
An imaging system projects a magnified image of this color-sequential (or color scrolling) picture onto a viewing surface where the viewer perceives a full-color image as a result of the human eye's slower response time compared with the rate of color modulation in the imaging system. Due to the color-sequential nature of the one-panel display, a lower-brightness image results as compared with three-panel displays. The image may also include color-breakup artifacts due to the temporal nature of the color sequencing system.
A two-panel architecture is a compromise between these two extremes. There are several schemes for color management in a two-panel architecture. In a first scheme, light from the illumination source is divided into two beams by splitting the raw light into its two constituent, orthogonal polarization states. Each of these beams is routed to one of the two imagers. Both of these two optical paths are modulated with color sequencing or color scrolling means, similar to systems having only a single imager.
The two resulting color-modulated images are recombined using a polarization beam combiner to create a single color-sequential full-color image. The benefit of this approach compared to a one-panel system is a brighter image than that obtained using only one imager. However this system is still not as bright as a three-panel system since some form of temporal color sequencing is still needed. For purposes of convenient discussion, this type of two-panel system shall hereinafter be referred to as a Polarization-Divided Color Sequential (alternatively “Color Scrolling”) (“PDCS”)-type two-panel system.
In a second scheme disclosed in U.S. Pat. No. 6,280,034 issued Aug. 28, 2001 to Brennesholtz, and U.S Pat. No. 6,388,718 issued May 14, 2002 to Yoo et al, light from the source is spectrally divided into two beams such that one of the beams consists of light from a single primary color channel (for instance only red light) and the second beam consists of light from the remaining two primary color channels (green and blue light, for example). The color system used herein will be the additive color system unless otherwise indicated, including indication by contextual use. In the additive color system, red, blue, and green are the primary colors, and magenta (red+blue), cyan (blue+green) and yellow (red+green) are the secondary colors. Those of skill in the art appreciate that magenta, cyan, and yellow are called primary colors in the subtractive color system, which is often used in describing printing systems, for example.
Light from the first beam is routed to one of the panels so that this panel continuously receives one primary illumination color and displays image data corresponding to this one primary color. The second beam, consisting of light from the two remaining primary colors, is directed to the second imaging panel. Color sequencing or color scrolling means are used to temporally sequence the two primary colors of the second beam onto the imaging panel.
The imaging panel is electronically addressed with a time-sequential video image data stream that modulates in synchrony with the time-varying (and possibly space-varying, e.g. scrolling) two-color illumination source.
The images from the two imaging panels are optically combined using a dichroic beam-combining element and are projected onto a screen or viewing surface to create a full-color image. This system may optionally include a polarization recovery subsystem in the illumination subsystem to increase overall display brightness. Nevertheless, the resulting image is less bright than a full three-panel system due to the temporal color sequencing in the two-color imager. However, it is typically brighter than a one panel system because it is capable of simultaneously projecting two overlapping, full-frame color images, whereas the single panel system only displays one full-frame color image at any instant in time. This latter type of two-panel system shall hereinafter be referred to as a Basic Color-Divided Color Sequential (or Color Scrolling) (“BCDCS”)-type two-panel system.
U.S. Pat. No. 5,517,340 issued May 14, 1996 to Doany et al, and U.S. Pat. No. 5,863,125 issued Jan. 26, 1999 to Doany disclose two-panel schemes in which color wheels are used to sequentially provide one of the primary colors to a polarization beam splitting cube for projection. Moreover, U.S. Pat. No. 6,568,815 issued May 27, 2003 to Yano et al, and U.S. Pat. No. 6,650,377 issued Nov. 18, 2003 to Robinson et al disclose dual-panel systems in which a series of active and passive polarizing filter stacks are used to control which primary and or secondary colors are provided to the panels.
An object of the present invention is to overcome the shortcomings of the prior art by providing a two-panel LCoS system in which both of the imagers are time-shared between two colors, and in which both polarized and unpolarized light can be used in the initial separation stages.